The present invention relates to a stepping motor control device for an automobile air-conditioning system, in particular, relates to a control device of a stepping motor for driving an air-conditioning door.
A device for controlling a stepping motor which is controlled by an open loop is shown in the Japanese Patent Laid Open Publication No. 1-206415. This publication shows, as an embodiment, a control of a stepping motor applied to a pump for supplying lubricating oil to an apex seal and a side seal of a rotary engine. This device detects whether or not a revolution of an engine is below an idling revolution (800 rpm), and resets the stepping motor which is controlled by an open loop to a home position each time when the number of cases with revolution below the idling revolution reaches a prescribed number. According to this, as the stepping motor is reset to the home position each time when the number of cases with revolution below the idling revolution reaches the prescribed number, positional slippage due to a step-out of the stepping motor can be corrected.
However, if a conventional system like this is applied to driving of an air-conditioning door, including an air-mix door, a mode door, etc. of an automobile air-conditioning system, such a home position resetting of a stepping motor for driving an air-conditioning door is reiterated during an air-conditioning control. The result is that a proper air-conditioning status cannot be attained. Because of this, in the case of a conventional automobile air-conditioning system for driving an air-conditioning door by a stepping motor which is controlled by an open loop, the air-conditioning door is always returned to a predetermined home position and the stepping motor is reset to the home position when a key switch is turned on. A normal air-conditioning control is started only after the stepping motor has been reset to the home position.
According to a conventional automobile air-conditioning system like this, a rise of air-conditioning when a key switch is turned on is delayed, because, even when the key switch is turned on, air-conditioning is started only after the air-conditioning door has been returned to the predetermined home position and the stepping motor has been reset to the home position. Thus, there is a problem from a viewpoint of attaining an optimal air-conditioning of a car-room within as short a time as possible.